Platinum Oxide Catalyzed Hydrosilylation of Unsymmetrical Internal Aryl Alkynes under Ortho-Substituent Regiocontrol
摘要:
[GRAPHICS]PtO2- and H2PtCl6-catalyzed hydrosilylation of internal aryl alkynes having a para or an ortho substituent with triethylsilane are discussed and compared. The regioselectivity of the H-Si bond addition was found to be controlled by the ortho substituent rather than the nature of the platinum catalyst. Arylallcynes with an ortho substituent, regardless of its electronic nature, directed the silyl substituent mainly to the a-position. PtO2 proved to be a versatile and powerful catalyst compared to H2PtCl6 since it prevents the alkyne reduction.
[GRAPHICS]PtO2- and H2PtCl6-catalyzed hydrosilylation of internal aryl alkynes having a para or an ortho substituent with triethylsilane are discussed and compared. The regioselectivity of the H-Si bond addition was found to be controlled by the ortho substituent rather than the nature of the platinum catalyst. Arylallcynes with an ortho substituent, regardless of its electronic nature, directed the silyl substituent mainly to the a-position. PtO2 proved to be a versatile and powerful catalyst compared to H2PtCl6 since it prevents the alkyne reduction.
Regiochemical Aspects of the Platinum Oxide Catalyzed Hydrosilylation of Alkynes
The platinum-catalyzed hydrosilylation of unsymmetrical substituted arylalkynes with various hydrosilanes was investigated and the reaction selectivity of various para-substituted substrates was compared with that of their corresponding ortho-substituted derivatives. We showed that heterogeneous platinum oxide is a very efficient catalyst for such hydrosilylations and that H-Si bond addition proceeds in a stereoselective cis-fashion. The regioselectivity was found to be under the control of the ortho-substituent rather than due to the nature of the platinum catalyst. Arylalkynes with an ortho-substituent provided predominantly to exclusively α-selectivity, regardless of the electronic nature of the substituent. The precise contributions of steric, electronic, and coordinative factors controlling the regioselectivity of the H-Si bond addition are discussed.